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Sex Differences in a Transgenic Rat Model of Huntington's Disease

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Sex Differences in a Transgenic Rat Model of Huntington's Disease Human Molecular Genetics, 2008, Vol. 17, No. 17 2595–2609 doi:10.1093/hmg/ddn159 Advance Access published on May 23, 2008 Sex differences in a transgenic rat model of Huntington’s disease: decreased 17b-estradiol levels correlate with reduced numbers of DARPP321 neurons in males 1,{ 1,{ 1 1 2 Felix J. Bode , Michael Stephan , Hendrik Suhling , Reinhard Pabst , Rainer H. Straub , Downloaded from https://academic.oup.com/hmg/article-abstract/17/17/2595/632381 by guest on 27 June 2020 Kerstin A. Raber3, Michael Bonin4, Huu Phuc Nguyen4, Olaf Riess4, Andreas Bauer5,6, Charlotte Sjoberg7,A˚ sa Peterse´n7 and Stephan von Ho¨ rsten1,3,Ã 1Institute of Functional and Applied Anatomy, Medical School of Hannover, 30625 Hannover, Germany, 2Department of Internal Medicine I, University Regensburg, 93042 Regensburg, Germany, 3Experimental Therapy, Franz-Penzoldt- Center, Friedrich-Alexander-University Erlangen-Nu¨rnberg, 91054 Erlangen, Germany, 4Department of Medical Genetics, University of Tu¨bingen, 72076 Tu¨bingen, Germany, 5Institute of Neurosciences and Biophysics, Research Centre Juelich, 52425 Juelich, Germany, 6Department of Neurology, Heinrich-Heine University Duesseldorf, 40001 Duesseldorf, Germany and 7Translational Neuroendocrine Research Unit, Department of Experimental Medical Science, Lund University, 22184 Lund, Sweden Received March 10, 2008; Revised May 8, 2008; Accepted May 21, 2008 Recent clinical studies have highlighted that female sex hormones represent potential neuroprotective mediators against damage caused by acute and chronic brain diseases. This evidence has been confirmed by experimental studies documenting the protective role of female sex hormones both in vitro and in vivo, although these studies did not specifically focus on Huntington’s disease (HD). We therefore investigated the onset and course of HD in female and male transgenic (tg) HD (CAGn51) and control rats across age and focused on three aspects: (i) behavioral and physiological alterations (energy expenditure, home-cage activity, emotional disturbance and motor dysfunction), (ii) morphological markers (numbers and characteristics of striatal DARPP321 medium-sized spiny neurons (MSNs) and dopamine receptor autoradiography) and (iii) per- ipheral sex hormone levels as well as striatal estrogen receptor expression. Independent of their sex, tgHD rats exhibited increased levels of food intake, elevated home-cage activity scores and anxiolytic-like behavior, whereas only males showed an impairment of motor function. In line with the latter finding, loss and atrophy of DARPP321 MSNs were apparent only in male tgHD rats. This result was associated with a decreased striatal dopamine D1 receptor density and lower plasma levels of 17b-estradiol at the age of 14 months. As DARPP321 MSNs expressed both a-andb-estrogen receptors and showed a correlation between cell numbers and 17b-estradiol levels, our findings suggest sex-related differences in the HD phenotype pointing to a substantial neuroprotective effect of sex hormones and opening new perspectives on the therapy of HD. INTRODUCTION striatal neurodegeneration (2). The clinical triad of motor dys- function, cognitive decline and psychiatric manifestations Huntington’s disease (HD) is a polyglutamine disorder based on characterizes HD. Owing to its autosomal-dominant inheri- an expanded CAG triplet repeat (1) leading to cerebral and tance, the prevalence is equally distributed between both ÃTo whom correspondence should be addressed at: Experimental Therapy, Franz-Penzoldt-Center, Friedrich-Alexander-University Erlangen-Nu¨rnberg, Palmsanlage 5, 91054 Erlangen, Germany. Tel: þ49 91318523504; Fax: þ49 91318523502; Email: [email protected] †The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors. # The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected] 2596 Human Molecular Genetics, 2008, Vol. 17, No. 17 sexes (3,4). However, potential sex differences concerning the life, there was a parallel weight gain in male tgHD rats and age of onset and the course of the disease are poorly defined, controls. In later life, male tgHD rats showed a trend as difficulties of matching female and male HD patients regard- towards lower body weights (Fig. 1), in line with previous ing their CAG repeat lengths limit comparability. There are reports (13). In contrast, two factorial analysis of variance only few reports focusing on this issue, suggesting that the (ANOVA) for repeated measurements revealed a significant age of onset of HD is higher (5) and the course of disease is effect for the factor genotype, as female tgHD rats gained more moderate (6) in women compared with men. Analogously, more weight than controls (F1,270 ¼ 4.3, P , 0.05). This was sexual dimorphisms regarding the prevalence and severity of mainly due to an increased weight gain in the first 4 months disease have also been reported for other neurodegenerative of life (Fig. 1). diseases, e.g. Parkinson’s and Alzheimer’s disease (7). To investigate whether this altered weight gain was associ- Thus, although clinical studies provide clear evidence that ated with differences in feeding behavior, we determined the female sex hormones exert neuroprotective effects in acute individual daily food intake. Although ANOVA for the Downloaded from https://academic.oup.com/hmg/article-abstract/17/17/2595/632381 by guest on 27 June 2020 and chronic brain diseases, this has not been unequivocally factor genotype showed a significantly increased absolute documented in HD (8,9). Likewise, experimental studies doc- food consumption (F1,216 ¼ 12.1, P , 0.01) as well as relative umenting a protective role of female sex hormones both in food intake in female tgHD rats as compared with controls vitro and in vivo have so far not specifically focused on HD (Fig. 1C and E; F1,216 ¼ 7.9, P , 0.05), the relative food (10,11). In order to examine sex-related differences in HD, intake (%/body weight) was significantly elevated only in animal models provide a useful approach to study sex differ- tgHD males compared with wild types (Fig. 1D and F; ences, because they allow the circumventing of the problems F1,216 ¼ 14.1, P , 0.01). Thus, male rats ingested more food of standardization, which are regularly occurring in humans. absolutely (P , 0.0001), but ate significantly less compared We therefore investigated the phenotype of male and female with females in relation to their body weight (P , 0.0001). transgenic (tg) HD rats carrying 51 CAG repeats under the Analyzing the indirect calorimetry using a dedicated calori- control of the endogenous rat huntingtin promoter (12). In metric system (TSE LabMaster system) revealed significant this HD model, male animals exhibit a progressive neuro- sex differences (ANOVA for repeated measurements: pathological phenotype closely resembling the most common F1,2280 ¼ 28.4, P , 0.0001) with female tgHD rats showing late manifesting type in human HD (13). However, a few a trend towards increased calorimetric exchange rate (kcal/h/ studies using only female rats have suggested a blunted pheno- kg) (F1,1216 ¼ 3.9, P ¼ 0.06, n.s.) (figures illustrating VO2, type in female tgHD (14–16), but this was not directly com- VCO2 and consecutive calorimetric measures are available pared with an additional male cohort. online). We therefore aimed to characterize the behavioral phenotype The diurnal baseline activity in the home-cage environment of female tgHD compared with their male counterparts as well was monitored. Here, male rats tg for HD showed an elevated as control littermates across age. Here, the focus was on activity compared with controls. This was detectable at all energy expenditure, activity in the home-cage, emotional dis- time points investigated, whereas females did not show turbance within the social interaction test as well as motor dys- significant hyperactivity until the age of 4 months. In later function using the accelerod test. As female tgHD rats showed life, tgHD females showed a dramatically increased most of the behavioral abnormalities seen in males, the most hyperactivity, whereas female wild-types and both tgHD and prominent difference was a lack of motor impairments in wild-type males remained on moderate activity levels females. As the striatum plays a key role in the coordination (Fig. 2). As exemplified in Figure 2 for the different ages, of motor function and is one of the key brain areas affected in ANOVA for repeated measurements with the interindividual HD (2), we focused on possible morphological alterations in factor genotype and the intraindividual factor ‘activity over the striatum by means of stereology of medium-sized spiny time’ revealed significant effects for young rats (females: neurons (MSNs) expressing dopamine- and cAMP-regulated F1,1566 ¼ 1.6, P , 0.001; males: F1,1566 ¼ 1.7, P , 0.0001) þ phosphoprotein of 32 kDa (DARPP32 ), dopamine receptor as well as for 14-month-old rats (females: F1,1566 ¼ 7.5, expression and concomitant changes in sex hormone plasma P , 0.0001; males: F1,1566 ¼ 1.5, P , 0.01). To illustrate levels. Our findings and conclusions were compared with a this hyperactivity, videotapes highlighting genotype- re-analysis of publicly available gene-expression profiling dependent effects on the home-cage activity in tgHD rats data from HD patients and controls (17), which were split by compared with wild-types at the age of 8 months
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